West Nile Disease has developed as a major mosquito borne health problem in the United States. No therapy is known to be effective. Animal models suggest that immune serum may be beneficial. A national protocol has been developed in collaboration with the NIAID: Collaborative Antiviral Study Group to study the efficacy of high titer immunoglobulin, obtained from Israel, compared to appropriate placebos. The study is randomized and double blinded. It has opened at 60 centers in the United States and Canada including the Clinical Center. Thirty-nine patients have been enrolled to date, including two at the Clinical Center. This protocol is a model for intramural-extramural collaboration to meet the challenge of a new, emerging infection. This study has been hampered by the dearth of US cases in 2005 and 2006. The study will terminate in October 2006 and data will be assessed to determine what can be learned from the small number of cases acrrued.